/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if (!head)
            return head;
        ListNode* newHead = head;
        ListNode* headNext = newHead->next;
        
        while (headNext)
        {
            ListNode* tmp = headNext->next;
            headNext->next = newHead;
            newHead = headNext;
            headNext = tmp;
        }
        head->next = nullptr;
        return newHead;
        
    }
};